Photochromic naphthacenequinones, process for their preparation and the use thereof

ABSTRACT

Compounds of formula V,   &lt;IMAGE&gt; (V)  wherein R is unsubstituted C6-C14aryl or C6-C14aryl which is substituted by C1-C12alkyl, C1-C12alkoxy, C1-C12alkylthiol, phenyl, benzyl, -CN, -CF3, halogen or -COOR5, and R5 is H, C1-C18alkyl, cyclohexyl, cyclopentyl, phenyl, C1-C12alkylphenyl, benzyl or C1-C12alkylbenzyl, and at least one of the substituents R1 to R4 is an organic thiol, sulfoxyl or sulfonyl group, and the other members R1 to R4 are H, F, Cl or Br, are reversible photochromic systems which can be used for contrast formation or light absorption.

This is a divisional of Ser. No. 07/880,458, filed May 8, 1992, now U.S.Pat. No. 5,206,395 which is a divisional of Ser. No. 07/639,463, filedJan. 10, 1991, now U.S. Pat. No. 5,177,227.

The present invention relates to naphthacene-6,11-andnaphthacene-5,12-diones which are substituted in position 5,12 and 6,11by aryloxy groups and in positions 2, 3, 8 and/or 9 by at least oneorganic thiol, sulfoxyl or sulfonyl group, to corresponding 5,12- and6,11-dichloronaphthacenediones containing thiol groups, to a process forthe preparation of said aryloxy-substituted naphthacenediones, and tothe use thereof as photochromic systems for contrast formation or lightabsorption.

In Zhurnal Organicheskoi Khimii, Vol. 7, No. 11, pp. 2413-2415 (1971),Yu. E. Gerasimenko et al. describe 6-phenoxynaphthacene-5,12-dione as areversible photochromic compound which, when subjected to irradiationwith light, forms the orange 5-phenoxynapthacene-6,12-dione(anaquinone). In Zhurmal Organicheskoi Khimii, Vol. 16, No. 9, pp.1938-1945 (1980), Yu. E. Gerasimenko et al. describe6,11-diphenoxynaphthacene-5,12-dione, whose photoisomerisation is usedfor synthesising 6-amino derivatives of12-phenoxynaphthacene-5,11-dione.

In one of its aspects, the present invention relates to compounds offormula I, or mixtures thereof, ##STR2## wherein R is unsubstituted C₆-C₁₄ aryl or C₆ -C₁₄ aryl which is substituted by C₁ -C₁₂ alkyl, C₁ -C₁₂alkoxy, C₁ -C₂ alkylthiol, phenyl, benzyl, --CN, --CF₃, halogen or--COOR₅, and R₅ is H, C₁ -C₁₈ alkyl, cyclohexyl, cyclopentyl, phenyl, C₁-C₁₂ alkylphenyl, benzyl or C₁ -C₁₂ alkylbenzyl, and at least one of thesubstituents R₁ to R₄ is an organic thiol, sulfoxyl or sulfonyl group,and the other members R₁ to R₄ are H, F, Cl or Br.

R in formula I is preferably unsubstituted or substituted C₆ -C₁₀ arylsuch as phenyl, or 1-or 2-naphthyl. Preferably R is unsubstituted orsubstituted phenyl.

The group R may be substituted by one or more, preferably by 1 to 3,substituents. If R is substituted by alkyl, alkoxy or alkylthiol, theseradicals may be linear or branched and preferably contain 1 to 6, mostpreferably 1 to 4, carbon atoms. Exemplary of such radicals are methyl,ethyl, the isomers of propyl, butyl, pentyl, hexyl, heptyl, octyl,nonyl, decyl, and the corresponding alkoxy and alkylthiol radicals.Preferred radicals are methyl, ethyl, n- and isopropyl, n-, iso- andtert-butyl, methoxy, ethoxy, methylthiol and ethylthiol.

If R is substituted by halogen, preferred halogens are bromo, chloro andfluoro.

R₅ as alkyl may be linear or branched. Further examples of the alkylradicals mentioned above are the isomers of tridecyl, tetradecyl,pentadecyl, hexadecyl, heptadecyl and octadecyl. R₅ as alkyl preferablycontains 1 to 12, most preferably 1 to 6, carbon atoms. R₅ asalkylphenyl is preferably C₁ -C₆ alkylphenyl, most preferably C₁ -C₄alkylphenyl, for example dodecylphenyl, octylphenyl, hexylphenyl, n-,iso- or tert-butylphenyl, n- or isopropylphenyl, ethylphenyl ormethylphenyl. R₅ as alkylbenzyl is preferably C₁ -C₆ alkylbenzyl, mostpreferably C₁ -C₄ alkylbenzyl, for example dodecylbenzyl, octylbenzyl,hexylbenzyl, n-, iso- or tert-butylphenyl, n- or isopropylbenzyl,ethylbenzyl or methylbenzyl. R₅ is preferably H or C₁ -C₁₈ alkyl, mostpreferably C₁ -C₁₂ alkyl.

In a preferred embodiment of the invention, R in formula I isunsubstituted or substituted by C₁ -C₄ alkyl, C₁ -C₄ alkoxy, C₁ -C₄alkylthio, --F, --Cl, --Br or --COOR₅, and R₅ is H or C₁ -C₁₈ alkyl.

Another preferred embodiment of the invention relates to those compoundsof formula I, wherein at least one of R₁ to R₄ is an organic thiol,sulfoxyl or sulfonyl group and the other members R₁ to R₄ are H.

In yet a further preferred embodiment of the invention, R₁ or R₄, or R₁and R₃ or R₄, or R₁ and R₂, or R₁ to R₄ are an organic thiol, sulfoxylor sulfonyl group. The organic thiol, sulfoxyl and sulfonyl grouppreferably contains 1 to 30, more particularly 1 to 20 and, mostpreferably, 1 to 12 carbon atoms. R₁ to R₄ are preferably an organicthiol group. Preferred compounds of formula I are those wherein theorganic thiol, sulfoxyl or sulfonyl group has the formula R₆ S--, R₆SO-- or R₆ SO₂ --, wherein R₆ is C₁ -C₂₀ alkyl, C₃ -C₈ cycloalkyl, C₃-C₈ cycloalkylmethyl, C₆ -C₁₀ aryl or C₆ -C₁₀ arylmethyl, and R₆ isunsubstituted or substituted by halogen, --CN, --CF₃, --COOR₅, C₁ -C₁₂alkyl, C₁ -C₁₂ alkoxy or C₁ -C₁₂ alkylthiol, and R₅ has the meaningsgiven above. The organic group is preferably a group of formula R₆ S--.

R₆ may be unsubstituted or may carry one or more, preferably one tothree, substituents. If the substituent is halogen, it is preferablyfluoro, chloro or bromo. Preferred substituents of R₅ are thosespecified above. If the substituent is alkyl, alkoxy or alkylthiol, saidradicals preferably contain 1 to 6, most preferably 1 to 4, carbonatoms. Exemplary of such radicals are those cited above.

In a preferred embodiment of the invention, R₆ is unsubstituted orsubstituted by C₁ -C₄ alkyl, C₁ -C₄ alkoxy, --F, --Cl or --COOR₅, and R₅is H or C₁ -C₁₈ alkyl.

R₆ as linear or branched alkyl preferably contains 1 to 18 and,preferably, 1 to 12 carbon atoms. Examples of such radicals are citedabove. R₆ as alkyl is preferably substituted by --COOR₅ and thencontains in the alkyl moiety preferably 1 to 4, most preferably 1 or 2,carbon atoms. Exemplary of such radicals are R₅ OOC--CH₂ S-- and R₅OOC--CH₂ CH₂ S--.

R₆ as cycloalkyl preferably contains 4 to 7, most preferably 5 or 6,ring carbon atoms. Such radicals are typically cyclopropyl, cyclobutyl,cycloheptyl, cyclooctyl and, preferably, cyclopentyl and cyclohexyl.

R₆ as cycloalkylmethyl preferably contains 3 to 7, most preferably 5 or6, ring carbon atoms, and is preferably cyclopentylmethyl andcyclohexylmethyl.

R₆ as aryl may be 1- or 2-naphthyl and, preferably, phenyl.

R₆ as arylmethyl may be naphthylmethyl and, preferably, benzyl.

In a preferred embodiment of the invention, R₆ is unsubstituted orsubstituted C₁ -C₁₂ alkyl, phenyl or benzyl.

Particularly preferred compounds of formula I are those wherein R₆ is C₁-C₁₂ alkyl or C₁ -C₄ alkyl which is substituted by --COOR₅, or is phenylor benzyl, each unsubstituted or substituted by --F, --Cl, C₁ -C₄ alkyl,C₁ -C₄ alkoxy or --COOR₅, and R₅, is H or C₁ -C₁₈ alkyl.

In another of its aspects, the present invention relates to a processfor the preparation of compounds of formula I, which comprises reacting(a) a compound of formula II ##STR3## wherein at least one of R₁, R₂, R₃and R₄ is an organic thiol group and the other members R₁ to R₄ are H,F, Cl or Br, in the presence of a polar aprotic solvent and at elevatedtemperature, with a compound of formula RO.sup.⊖ M.sup.⊕, wherein R isas previously defined and M is an alkali metal, and (b) oxidising theresultant compounds, in a manner known per se, to compounds of formula Icontaining organic sulfoxyl or sulfonyl groups.

The process of the invention is preferably carried out in thetemperature range from 50° to 200° C., most preferably from 50° to 150°C. The salts of formula RO.sup.⊖ M.sup.⊕ may be used as such or producedin situ in the reaction mixture by reacting a suitable phenol with analkali metal base or an alkali metal carbonate. The salts can be used inequimolar amounts or in excess, for example in an excess of up to 40 mol%.

Typical examples of suitable solvents are N-substituted carboxamides andlactams (such as dimethyl formamide or N-methylpyrrolidone), sulfoxidesand sulfones (such as dimethyl sulfoxide, tetramethylene sulfone), orethers (such as n-dipropyl ether, n-dibutyl ether, tetrahydrofuran ordioxane).

The oxidation of process step (b) can be carried out with alkali metalperoxides, organic peroxides and, preferably, H₂ O₂. The reaction isnormally carried out in a solvent, preferably glacial acetic acid. Thereaction temperature may be in the range from room temperature to 150°C., preferably to 100° C.

The compounds of formula I can be isolated and purified by conventionalmethods, for example by crystallisation and recrystallisation, or bychromatographic methods.

The compounds of formula RO.sup.⊖ M.sup.⊕ are known or obtainable inknown manner by reacting suitable phenols with alkali metal bases oralkali metal carbonates. Particularly suitable alkali metal cations areLi.sup.⊕, Na.sup.⊕ und K.sup.⊕. ##STR4## wherein at least one of R₁ toR₄ is an organic thiol group and the others are H, --F, --Cl or --Br.The preferred meanings of R₁ to R₄ are the same as those given for thecompounds of formula I.

The compounds of formula I are obtainable by the following process:

The reaction of the known compounds of formula III ##STR5## wherein atleast one X is halogen, preferably fluoro or chloro, and the othersubstituents X are halogen or hydrogen, with organothiols of formula R₁SH, R₂ SH, R₃ SH and/or R₄ SH gives the compound of formula IV which,when unsymmetrically substituted, is obtained as a mixture of tautomersof formulae IV and IVa: ##STR6##

These mixtures of tautomers can be used direct for the preparation ofcompounds of formula II or separated beforehand, for example bychromatographic methods. The nucleophilic substitution can also becarried out with the corresponding thiolate ions, for example the alkalimetal salts, preferably lithium, sodium and potassium salts. Thecompounds of formula III are obtainable, for example, by reactingappropriately halogenated or non-halogenated phthalic anhydrides withappropriately halogenated or non-halogenated 1,4-dihydroxynaphthalene,in the presence of B₂ O₃, at elevated temperature.

The compounds of formula IV and IVa can be converted into the compoundsof formulae II with customary chlorinating agents such as POCl₃.

The compounds of formula I, wherein R₁ to R₄ are at least one organicthiol group, can also be prepared by chlorinating the compounds offormula III with chlorinating agent first to compounds of formula VI##STR7## for example with POCl₃ in the temperature range from 50° to200° C. and in the presence of a solvent such as dichlorobenzene,reacting the compounds of formula VI, in the presence of a solvent andan alkali metal carbonate in the temperature range from 50° to 200° C.,with not less than 3 mol of R₁ SH and, if desired, with at least 1 molof R₂ SH, R₃ SH and/or R₄ SH per mol of compound of formula VI tocompounds of formula VII ##STR8## wherein R₁ is an organic thiol groupand R₂ to R₄ are an organic thiol group, --H, --F, --Cl or --Br, andthen reacting the compounds of formula VII, under oxidative conditionsand in the presence of a solvent and an alkali metal carbonate, with aphenol ROH to compounds of formula I. Suitable solvents are thosepreviously mentioned. Preferred alkali metal carbonates are sodiumcarbonate and, preferably, potassium carbonate. By the expression"oxidative conditions" is meant preferably the presence of air.Surprisingly, in this process only the organic thiol groups R₁ aresubstituted in the positions 5 and 11 regioselectively by phenol groups.The process is conveniently used for the preparation of compounds offormula I, wherein R₁ to R₄ are organic thiol groups.

The compounds of formula I are crystalline, thermally stable and yellowto orange in colour. They are soluble in organic solvents. They areeffective photoinitiators and photosensitisers for photopolymerisablesystems which contain ethylenically unsaturated double bonds. Further,the compounds of formula I are reversibly photochromic.

When the compounds of formula I are irradiated, alone or incorporated ina substrate, with light having a wavelength of ca. 300 to 450 nm, apronounced change in colour towards red is observed. In comparison with6,11-diphenoxynaphthacene-5,12-dione, the light absorption is displacedto a higher wavelength. The change in colour derives from thephotochemical conversion of the paraquinones of this invention into thecorresponding anaquinones of formula V. The rate of conversion issurprisingly high and, depending on the amount, thickness of the sampleand irradiation intensity, can be less than 3 seconds.

The invention further relates to the anaquinones of formula V ##STR9##wherein R, R₁, R₂, R₃ and R₄ are as previously defined, including thepreferred meanings.

The compounds of formula V can be obtained, after irradiating solutionsof the compounds of formula I, by removing the solvent, and, asrequired, purified by conventional methods.

The change in colour is reversible. Renewed irradiation with lighthaving a wavelength of ca. 450 to 550 nm gives the original colour(reformation of the paraquinone structure). It is especiallyadvantageous that this procedure can be repeated several times. Thestability of the photochemical conversion of paraquinones to anaquinonesand the reverse reaction to paraquinones is surprisingly high and thefatigue even in air or in substrates is correspondingly low. Thusvirtually no changes are observed in more than 200 cycles. It is alsoadvantageous that the light absorption necessary for the photochemicalconversion lies in the range of the wavelength of commercially availablelasers.

The invention further relates to the use of compounds of formula I or Vas reversible photochromic structures for contrast formation or lightabsorption.

The compounds of formula I can be used as photoinitiators and,preferably, as photosensitisers in photopolymerisible systems, in whichcase they act simultaneously as colour indicators. Thus it is possibleto mark irradiated products (for example protective layers, printingplates, offset printing plates, printed circuits, solder masks) and todistinguish them from non-irradiated products and, in product control,to sort out imperfectly irradiated products before or after development.

The major advantage in using the compounds of formula I as colourindicators lies in the increase of the sensitiser action. Componentsnormally used as colour change systems generally effect a diminution ofthe photosensitivity.

The compounds of formula I or V can also be used by themselves, insolution or incorporated in polymers as photochemically modifiablecolour indicators or as photochemically modifiable circuit components.

The compounds of formula I can also be used in organic or inorganicglass as photochemically modifiable colour filters, for example in glassfor sunglasses, contact lenses, windows and mirrors.

The invention further relates to a radiation-sensitive compositioncomprising

a) a radiation-sensitive organic material, and

b) at least one compound of formula I or V or a mixture thereof.

The compounds of formulae I and V or mixtures thereof may be present inan amount of 0.001 to 20% by weight, preferably 0.001 to 10% by weightand, most preferably, 0.01 to 5% by weight, based on component a).

Radiation-sensitive and hence also photostructurable materials areknown. They may be positive or negative systems. Such materials aredescribed, for example, by E. Green et al. in J. Macromol. Sci.; Revs.Macromol. and Chem., C21(2), 187-273 (1981 to 1982) and by G. A.Delzenne in Adv. Photochem., 11, S. 1-103 (1979).

The radiation-sensitive organic material is preferably a1) anon-volatile monomeric, oligomeric or polymeric substrate containingphotopolymerisable or photodimerisable ethylenically unsaturated groups,a2) a cationically curable system, or a3) photocrosslinkable polyimides.

Photopolymerisable substances are typically acrylates and, preferably,methacrylates of polyols, for example ethylene glycol, propanediol,butanediol, hexanediol, bis(hydroxymethyl)cyclohexane,polyoxyalkylenediols such as di-, tri- or tetraethylene glycol, di- ortri-1,2-propylene glycol, trimethylolmethane, trimethylolethane ortrimethylolpropane and pentaerythritol, which may be used by themselves,in mixtures and in admixture with binders.

Exemplary of photodimerisable substances are homo- and copolymers whichcontain cinnamic acid groups or substituted maleimidyl compounds in sidegroups or chalcone groups in the polymer chain.

Preferred compositions are those wherein component a1) is a homo- orcopolymer of acrylates, methacrylates or maleates whose ester groupscontain a radical of formula ##STR10## wherein A is linear or branchedunsubstituted or hydroxyl-substituted C₂ -C₁₂ alkylene, cyclohexylene orphenylene, and R₇ and R₈ are each independently of the other chloro orbromo, phenyl or C₁ -C₄ alkyl, or R₇ and R₈, when taken together, aretrimethylene, tetramethylene or ##STR11## Such polymers are disclosed,for example, in U.S. Pat. No. 4,193,927.

The photopolymerisable or photodimerisable substances can containfurther additives customarily used for processing or application, aswell as other photoinitiators or photosensitisers.

The cationically curable systems are preferably epoxy compoundscontaining at least two epoxy groups in the molecule and in which aphotoinitiator is incorporated. Suitable photoinitiators are typicallycyclopentadienylarene metal salts, cyclopentadienyl metal carbonyl saltsand onium salts which are described in the above mentioned publications.The curable systems may contain additives customarily used forprocessing and application.

Photosensitive polyimides are disclosed, for example, in DE-A-1 962 588,EP-A-0 132 221, EP-A-0 134 752, EP-A-0 162 017, EP-A-0 181 37 and EP-A-0182 745.

The composition of this invention is applied by known methods as layerto substrates and either a protective layer is produced by irradiationover the surface, or a relief image is produced by irradiation through aphotomask or by locally defined irradiation with a guided laser beam orby holographic methods and subsequent development.

In another of its aspects, the invention relates to a compositioncomprising a) a colourless organic solvent, a polymer or an organicglass or a compound glass, and b) dissolved, incorporated therein orpresent as layer on at least one surface, a compound of formula I or Vor a mixture thereof. Component b) is preferably present in an amount of0.001 to 20% by weight, preferably 0.001 to 10% by weight and mostpreferably, 0.01 to 5% by weight, based on component a). Organicsolutions can be used for coating other substances, for example solidsubstrates such as inorganic glasses which can then be used asphotochemically modifiable substrates. The compounds of formula I canalso be sublimed on to substrates. The coated substrates can be providedwith a protective layer of, for example, transparent polymers. Solidsubstrates can also be coated with compositions which contain a polymerand at least one compound of formula I or V. Suitable solvents aretypically hydrocarbons, halogenated hydrocarbons, ketones, carboxylicacid esters and lactones, N-alkylated acid amides and lactams, alkanolsand ethers.

Exemplary of suitable polymers are thermoset plastics, thermoplasticsand structurally crosslinked polymers. The polymers are preferablytransparent. Such polymers and organic glasses are known to thoseskilled in the art. The incorporation of the compounds of the inventionis effected by known methods, for example by dissolving methods andremoving the solvent, calendering or extrusion. The compounds of thisinvention can also be incorporated in the substrates before, during orafter their synthesis.

The invention also relates to a process for the preparation of colouredmaterials under the influence of light, which comprises incorporating acompound of formula I or V in the material and then irradiating saidmaterial with light.

The invention further relates to the use of compounds of formula I asphotosensitisers and colour indicators or photochemically modifiablecolour filters under the influence of light.

In another of its aspects, the invention relates to the use of acompound of formula I or V for the reversible optical storage ofinformation, which information is written with light, preferably laserlight, into a memory-active layer containing said compound. The writteninformation can be erased, preferably with laser light, thus affordingthe possibility of cyclic writing-in and erasing.

To produce a memory-active layer, the compound of formula I or V can bedissolved in a transparent matrix by methods described above and appliedin a thin layer to a flat substrate. The thickness of the memory-activelayer is ca. 0.1-100 μm, preferably 0.3-3 μm.

The information can be written by scanned, holographic or photographicirradiation of the memory-active layer with spectral, preferablycoherent, laser light in the wavelength range of 440-550 nm, preferably480-530 nm.

Reading out can be effected with reduced irradiation intensity at thewavelength in which the information is written via the locally alteredtransmission, reflectance, refraction or fluorescence of thememory-active layer.

Erasure can be made by pin-point or spread irradiation of thememory-active layer containing the compounds of formula I and/or V inthe wavelength range of 300-450 nm, preferably 300-400 nm.

One advantage of the utility of this invention is that the wavelengthsnecessary for writing in, reading out and erasing are in the range ofcommercially available lasers (for example argon ion lasers: 488/514 nmand 351/363 nm; neodym-YAG lasers: 532 nm and 355 nm; XeF excimerlasers: 351 nm; HeCd lasers: 325 and 442 nm, with frequency doubling andtrebling).

A further advantage is the high contrast of absorption obtainablebetween the written and erased state in the range of 450-550 nm and thewide dynamic range associated therewith of the memory-active layer.

Another advantage is that the quantum yield when writing is fairly low,so that the danger of overwriting when reading out is greatlydiminished.

Conversely, it is also advantageous that the quantum yield when erasingis fairly high, thus making possible a rapid erasure over a large area.

Yet a further advantage is that, when reading out, the compoundfluoresces and hence makes possible a highly sensitive detection of thememory status via the fluorescence. The fact that the energy pulsed infor reading out dissipates substantially via the fluorescence and notthermally also counteracts an undesirable heating of the memory-activelayer.

Another advantage is the high photochemical stability of the compoundand the great number of writing/erasing cycles thereby obtainable.

Finally, yet another advantage is the possibility of cyclic datarefreshing by admixture of a suitable quantum of light of the erasurewavelength during reading out.

The invention is illustrated by the following Examples.

A) Preparation of the starting compounds EXAMPLE A12,3,8,9-Tetraphenylthio-6,11-dihydroxynaphthacene-5,12-dione

50 g (116.8 mmol) of2,3,8,9-tetrachloro-6,11-dihydroxynaphthacene-5,12-dione, 77.22 g (700.8mmol) of thiophenol, 129.15 g (934 mmol) of potassium carbonate and 400ml of dimethyl sulfoxide (DMSO) are stirred for 1 day at 100° C. Themixture is poured into a dilute aqueous solution of HCl and stirred. Thered crude product is isolated by filtration, washed with water, dried at140° C. under vacuum, then extracted three times by boiling withcyclohexanone and dried once more. Yield: 80.11 g (95%); meltingpoint >260° C. MS: 722 (M⁺ ; base peak).

EXAMPLE A2 2,3,8,9-Tetraethylthio-6,11-dihydroxynaphthacene-5,12-dione

The title compound is prepared as described in Example A1 using ethylmercaptan. Yield: 89%; m.p.: 240° C. (decomposition); MS: 530 (M⁺ ; basepeak).

EXAMPLE A3 2,3,8,9-Tetra-n-dodecyl-6,11-dihydroxynaphthacene-5,12-dione

The title compound is prepared as described in Example A1, using dodecylmercaptan at 120° C. with the addition of dimethyl formamide (DMF):Yield: 87%; m.p.: 66°-76° C.; MS: 1090 (M⁺ ; base peak).

EXAMPLE A42,3,8,9-Tetra(p-methylphenylthio)-6,11-dihydroxynaphthacene-5,12-dione.

The title compound is prepared as described in Example A1 usingp-thiocresol at 100° C. Yield: 83%; m.p.: >265° C.; MS: 778 (M⁺ ; basepeak).

EXAMPLE 5A2,3,8,9-Tetra(p-chlorophenylthio)-6,11-dihydroxynaphthacene-5,12-dione.

The title compound is prepared as described in Example A1 usingp-chlorothiophenol at 120° C. Yield: 82%; m.p.: >300° C.; MS:858/860/862/864 (M⁺ ; base peak).

EXAMPLE A62,3,8,9-Tetra(3-methoxyphenylthio)-6,11-dihydroxynaphthacene-5,12-dione.

The title compound is prepared as described in Example A1 usingm-methoxythiophenol at 100° C. Yield: 90%; m.p.: 287°-92° C.; MS: 842(M⁺ ; base peak).

EXAMPLE 7A 2-Phenylthio-6,11-dihydroxynaphthacene-5,12-dione (mixture oftautomers)

4.62 g (15 mmol) of 2-fluoro-6,11-dihydroxynaphthacene-5,12-dione(mixture of tautomers), 2.2 g (20 mmol) of thiophenol, 11.06 g (80 mmol)of potassium carbonate and 50 ml of dimethyl sulfoxide (DMSO) arestirred for 22 hours at 70° C. The mixture is poured into 600 ml of a0.5M solution of HCl in H₂ O. After stirring for 15 minutes, theprecipitate is isolated by filtration, washed 3 times with water andonce with methanol, dried at 120° C. under vacuum and recrystallisedfrom toluene. Yield: 3.02 g (51%), m.p. >260° C.; MS: 398 (M⁺ ; basepeak), 388, 295, 261, 233, 199, 176.

The procedure of this Example is repeated, using2-chloro-6,11-dihydroxynaphthacene-5,12 dione (mixture of tautomers) andappropriately substituted thiophenols at 80° C., to give the compoundsA7a to A7e (mixtures of tautomers).

A7a: 2- and9-(4'-Chlorophenylthio)-6,11-dihydroxynaphthacene-5,12-dione. Yield:95%, m.p.: 225°-227° C.; mass spectrum: 432 (M⁺ ; base peak).

A7b: 2- and9-(4'-Fluorophenylthio)-6,11-dihydroxynaphthacene-5,12-dione. Yield:89%, m.p.: 192°-200° C.; mass spectrum: 416 (M⁺ ; base peak).

A7c: 2- and9-(4'-Methoxyphenylthio)-6,11-dihydroxynaphthacene-5,12-dione. Yield:84%, m.p.: 170°-175° C.; mass spectrum: 428 (M⁺ : base peak)

A7d: 2- and9-(4'-Ethoxycarbonylphenylthio)-6,11-dihydroxynaphthacene-5,12-dione.Yield: 95%, m.p.: 140°-150° C.; mass spectrum: 470 (M⁺ : base peak).

A7e: 2- and9-(3'-Methoxyphenylthio)-6,11-dihydroxynaphthacene-5,12-dione. Yield:90%, m.p.: 145°-155° C.; mass spectrum: 428 (M⁺ : base peak).

EXAMPLE 8 2-n-Dodecylthio-5,11-dihydroxynaphthacene-5,12-dione (mixtureof tautomers)

1.54 g (5 mmol) of 2-fluoro-5,11-dihydroxynaphthacene-5,12-dione(mixture of tautomers), 5.53 g (40 mmol) of K₂ CO₃, 2.02 g (10 mmol) ofn-dodecanethiol and 15 ml of DMSO are stirred for 18 hours at 90° C. Themixture is poured into a dilute aqueous solution of HCl. The mixture isstirred for 10 minutes and the product is then isolated by filtration,washed 3 times with water and once with methanol, dried at 80° C. undervacuum and recrystallised from toluene. Yield: 2.40 g (98%), m.p.146°-148° C.; MS: 398 (M⁺ : base peak), 388, 295, 261, 233, 199, 176.

EXAMPLE A9 2,3,6,8,9,11-Hexachloronaphthacene-5,12-dione

30 g (70 mmol) of2,3,8,9-tetrachloro-6,11-dihydroxynaphthacene-5,12-dione, 60 ml of POCl₃and 500 ml of o-dichlorobenzene are stirred for 90 hours under reflux.Then excess POCl₃ together with the o-chlorobenzene is removed bydistillation until the volume of the reaction mixture is still ca. 300ml. After cooling, the precipitate is isolated by filtration, washedrepeatedly with water and aqueous sodium carbonate solution, dried andstirred in cyclohexane. The product is isolated by filtration and thendried. Yield: 28.6 g (88%), m.p.: >260° C.

B) Preparation of inventive compounds EXAMPLE B12,3,8,9-Tetraethylthio-6,11-bis(3,5-dichlorophen-1-oxy)naphthacene-5,12-dione

a) 0.30 g (0.57 mmol) of the compound of Example A2 are stirred underreflux in 20 ml of phosphoroxy chloride for 8 days. With cooling, thereaction mixture is poured into water and is stirred. The precipitate isisolated by filtration, washed with water and dried. Chromatography withcopious methylene chloride over silica gel gives 0.13 g (40%) of2,3,8,9-tetraethylthio-6,11-dichloro-naphthacene-5,12-dione, m.p. >260°C.; MS: 566/568/570 (base peaks, M⁺).

b) 0.07 g (0.12 mmol) of this compound, 0.05 g (0.31 mmol) of3,5-dichlorophenol, 0.07 g (0.49 mmol) of potassium carbonate and 3 mlof DMSO are stirred for 18 hours at 70° C. The mixture is poured intowater/toluene and the organic phase is dried over sodium sulfate andconcentrated by evaporation. The crude product (0.08 g; 80%) isyellowish orange. The following λ_(max) values are obtained (UV/VISspectrum, solution in toluene): 439, 466 und 495 nm. The crude productcontains a minor amount of2,3,8,9-tetraethylthio-6,12-bis(3,5-dichlorophen-1-oxy)naphthacene-5,11-dione.

EXAMPLE B2 2,3,8,9-Tetraethylthio-6,11-diphenoxynaphthacene-5,12-dione

a) Process a) of Example B1 is repeated, starting from the compound ofExample A1 with the addition of dichlorobenzene as solvent, at 160° C.,to give 2,3,8,9-tetraphenylthio-6,11-dichloronaphthacene-5,12-dione: MS:758/760/762 (base peaks, M⁺).

b) Process b) of Example B1 is repeated, reacting this compound withphenol to give the yellowish orange title compound. UV/VIS spectrum intoluene: λ_(max) =432 nm.

EXAMPLE B3 2-Phenylthio-6,11-diphenoxynaphthacene-5,12-dione (A) and9-phenylthio-6,11-diphenoxynaphthacene-5,12-dione (B)

a) 2.90 (7.28 mmol) of the compound of Example A7 are stirred underreflux in 29 ml of POCl₃ for 2 days. With efficient stirring, themixture is charged into 300 ml of ice-water and stirred. The suspensionis extracted with toluene and the organic phases are filtered, washedwith 2N NaOH solution, dried over sodium sulfate and concentrated byevaporation. Yield: 2.73 g (86%). Fractional crystallisation fromtoluene gives both isomers in pure form:

2-phenylthio-6,11-dichloronaphthacene-5,12-dione: 0.38 g; m.p. 201°-3°C.; MS: 434/436/438 (M⁺);

9-phenylthio-6,11-dichloronaphthacene-5,12-dione: 0.13 g; m.p. 181°-4°C.; MS: 434/436/438 (M⁺).

b) 2 g (4.59 mmol) of the crude product (mixture of isomers), 1.08 g(11.49 mmol) of phenol, 2.54 g (18.38 mmol) potassium carbonate and 15ml of DMSO are stirred for 40 minutes at 60° C. The mixture is cooled,taken up in THF/toluene and a dilute solution of HCl and extracted. Theorganic phases are washed twice with water, dried over sodium sulfateand concentrated by evaporation. Flash chromatography with methylenechloride over silica gel gives both isomers in pure form.

More rapidly eluting product:

Title compound A: 1.12 g of crude product recrystalliosed from toluene:0.78 g (31%), m.p. 160°-3° C.; MS: 550 (M⁺ /base peak).

More slowly eluting product

Title compound B: 0.77 g of crude product, recrystallised from toluene:0.72 g (29%), m.p. 150°-3° C.; MS (m/e): 550 (M⁺) (base peak).

EXAMPLES B4-B8

Process b) of Example B3 is repeated by reacting the mixture of isomersof Example B3a) with the appropriate phenol to give the isomericmixtures of the following compounds:

    ______________________________________                                         ##STR12##                                                                                      Mass             Melting                                                      spectrum Yield   point                                      R                 [M.sup.+ ]                                                                             [Y]     [°C.]                               ______________________________________                                         ##STR13##        862      94      Oel                                         ##STR14##        706      80      205-230° C.                          ##STR15##        618      77      228-245° C.                          ##STR16##        610      80      177-182° C.                          ##STR17##        686      74      215-234° C.                         ______________________________________                                    

EXAMPLE B9 2-n-Dodecylthio-6,11-diphenoxynaphthacene-5,12-dione (A) and9-n-dodecylthio-6,11-diphenoxynaphthacene-5,12-dione (B)

a) Process a) of Example B3 is repeated, using n-dodecyl mercaptan andthe mixture of tautomers of Example A8. Chromatographic separation ofthe crude product (yield 86%) over silica gel with toluene gives:

2-n-dodecylthio-6,11-dichloronaphthacene-5,12-dione: 0.29 g; m.p.120°-125° C.;

9-n-dodecylthio-6,11-dichloronaphthacene-5,12-dione: 0.29 g; m.p.113°-114° C.;

b) 0.20 g (0.38 mmol) of2-n-dodecylthio-6,11-dichloronaphthacene-5,12-dione, 0.09 g (0.95 mmol)of phenol, 0.21 g (1.52 mmol) of potassium carbonate and 2 ml of DMSOare stirred for 75 minutes at 60° C. The mixture is taken up in tolueneand extracted twice with toluene. The toluene phases are washed twicewith water, dried over sodium sulfate and concentrated by evaporation.Recrystallisation from ether/pentane gives 0.13 g (54%) of the titlecompound A, m.p. 165°-8° C.; MS: 642 (M⁺ ; base peak).

The title compound B is obtained in analogous manner from

9-n-dodecylthio-6,11-dichloronaphthacene-5,12-dione: Yield afterrecrystallisation from ether/pentane: 0.13 g (54%), m.p. 143°-5° C.; MS:642 (M⁺ ; base peak).

EXAMPLES B10-B14 Naphthacenediones containing substituted phenylthiogroups

The compounds A7a to A7e are chlorinated as in process B3a and reactedin accordance with process B3b with phenol to give the correspondingmixtures of isomers:

EXAMPLE B10 2- and9-(4'-Chlorophenylthio)-6,11-diphenoxynaphthacene-5,12-dione

a) 2- and 9-(4'-Chlorophenylthio)-6,11-diphenoxynaphthacene-5,12-dione:reaction time: 7 days, yield: 64%, mass spectrum: 468 (M⁺ : base peak).

b) Title compound: yield: 70%, m.p.: >250° C., mass spectrum: 584 (M⁺ :base peak).

EXAMPLE B11 2- and9-(4'-Fluorophenylthio)naphthacene-6,11-diphenoxynaphthacene-5,12-dione

a) 2- and 9-(4'-Fluorophenylthio)-6,11-dichloronaphthacene-5,12-dione:reaction time: 8 days, yield: 68%, mass spectrum: 452 (M⁺ : base peak).

b) Title compound: yield: 61%, m.p.: >250° C., mass spectrum: 568 (M⁺ :base peak).

EXAMPLE B12 2- and9-(4'-Methoxyphenylthio)-6,11-phenoxynaphthacene-5,12-dione

a) 2- and 9-(4'-Methoxyphenylthio)-6,11-dichloronaphthacene-5,12-dione:reaction time: 4 days, yield: 85%, mass spectrum: 464 (M⁺ : base peak).

b) Title compound: yield: 66%, m.p.: 200°-206° C., mass spectrum: 580(M⁺ : base peak).

EXAMPLE B13 2- and9-(4'-Ethoxycarbonylphenylthio)-6,11-diphenoxynaphthacene-5,12-dione.

a) 2- and9-(4'-Ethoxycarbonylphenylthio)-5,11-dichloronaphthacene-5,12-dione:reaction time: 7 days, yield: 25%, mass spectrum: 506 (M⁺ : base peak).

b) Title compound: yield: 83%, m.p.: 190°-210° C., mass spectrum: 622(M⁺ : base peak).

EXAMPLE B14 2- and9-(3'-Methoxyphenylthio)-6,11-diphenoxynaphthacene-5,12-dione

a) 2- and 9-(3'-Methoxyphenylthio)-6,11-dichloronaphthacene-5,12-dione:reaction time: 6 days, yield: 85%, mass spectrum: 464 (M⁺ : base peak).

b) Title compound: yield: 75%, m.p.: 160°-170° C., mass spectrum: 580(M⁺ : base peak).

EXAMPLE B15 of 2,3- and8,9-Di(phenylthio)-6,11-diphenoxynaphthacene-5,12-dione (mixture ofisomers)

a) 2,3- and 8,9-Diphenylthio-6,11-dihydroxynaphthacene-5,12-dione 5 g(13.9 mmol) of 2,3- and8,9-dichloro-6,11-dihydroxynaphthacene-5,12-dione, 3.37 g (30.6 mmol) ofthiophenol, 6,81 g (49.3 mmol) of K₂ CO₃ and 50 ml of dimethyl sulfoxideare stirred for 3 hours at 65° C. The mixture is charged to dilutehydrochloric acid and the red crystals are isolated by filtration,washed with water and dried at 120° C. under vacuum. Recrystallisationfrom toluene gives 4.5 g of product, m.p.>270° C.

b) 2,3- and 8,9-Diphenylthio-6,11-dichloronaphthacene-5,12-dione

2.5 g of the mixture of iosmers obtained in step a) and 45 ml of POCl₃are stirred under reflux for 4 days. The mixture is poured into waterand the crystals are isolated by filtration, washed repeatedly withwater and then dissolved in toluene. The separated organic phase iswashed with dilute aqueous sodium hydroxide and then with water,subsequently dried over sodium sulfate and concentrated by evaporation.After stirring the residue in toluene with the addition of alumina,followed by filtration and concentration, 1.8 g of yellow crystals ofm.p. 240°-243° C. are obtained.

c) 1.7 g (3.13 mmol) of the mixture of isomers obtained in step b), 0.74g (7.82 mmol) of phenol, 1.3 g (9.4 mmol) of potassium carbonate and 30ml of dimethyl sulfoxide are stirred for 1 hour at 85° C. The reactionmixture is then poured into dilute hydrochloric acid and the crystallineprecipitate is isolated by filtration and taken up in a 1:1 mixture oftetrahydrofuran/toluene. The organic phase is washed with water, driedover sodium sulfate and then concentrated by evaporation.Recrystallisation from toluene gives 1.14 g (55%) of the title compoundin the form of yellow crystals of m.p.>270° C., mass spectrum: 658 ((M⁺,base peak). A reversible change from yellowish orange to red is observedby irradiating a solution of the compound in toluene.

EXAMPLE B16 2,8- and2,9-Diphenylthio-6,11-diphenyloxynaphthacene-5,12-dione

a) 2,6,8,11- and 2,6,9,11-Tetrachloro-naphthacene-5,12-dione

20 g (55.8 mmol) of 2,8- and2,9-dichloro-6,11-dihydroxynaphthacene-5,12-dione (mixture oftautomers), 100 ml of POCl₃ and 400 ml of o-dichlorobenzene are heatedat reflux for 5 days. The reaction mixture is then concentrated to halfits volume and extracted with methylene chloride. The organic phase isseparated, washed with water and a saturated solution of sodiumchloride, dried over sodium sulfate and then concentrated byevaporation. The residue is chromatographed twice over silica gel andrecrystallised from xylene to give 11.2 g (51%) of product.

b) 2,6,8,11- and 2,6,9,11-Tetraphenylthionaphthacene-5,12-dione

2 g (5.05 mmol) of the mixture of isomers obtained in step a), 5.58 g(40.4 mmol) of potassium carbonate, 3.34 g (30.3 mmol) of thiophenol and14 ml of dimethyl sulfoxide are stirred for 1 day at 60° C. and for 4hours at 120° C. The reaction mixture is then poured into dilutehydrochloric acid and extracted with toluene. The organic phase iswashed with water, dried over sodium sulfate and concentrated byevaporation. The crude product is chromatographed over silica gel togive 1.38 g (40%) of the title compound in the form of a red oil.

c) 0.3 g (0.434 mmol) of the compound obtained in step b), 0.14 g (1.52mmol) of phenol, 0.24 g (1.74 mmol) of potassium carbonate and 10 ml ofdimethyl sulfoxide are stirred at 100° C. for 6 hours while introducingair. After cooling, the reaction mixture is taken up in toluene and theorganic phase is washed in succession with dilute hydrochloric acid, 1Naqueous sodium hydroxide and then with water, dried over sodium sulfateand concentrated by evaporation. The crude product is chromatographed,with the exclusion of light, with toluene over silica gel to give 0.12 g(43%) of the title compound in the form of an orange oil. Mass spectrum:658 (M⁺ : base peak). A reversible colour change from yellowish orangeto red is observed by irradiating a solution of the compound in toluene.

EXAMPLE B172,3,8,9,-Tetraphenylthio-6,11-diphenoxynaphthacene-5,12-dione

a) 2,3,6,8,9,11-Hexaphenylthionaphthacene-5,12-dione

10 g (21.5 mmol) of compound A9, 23.7 g (215 mmol) of thiophenol, 32.69g (237 mmol) of potassium carbonate and 200 ml of dimethyl sulfoxide arestirred for 18 hours at 80° C. After cooling, the reaction mixture ispoured into 2N hydrochloric acid and the precipitate is isolated byfiltration and washed with water. The crystalline precipitate isextracted repeatedly with hot cyclohexane and then dried, giving 16.8 g(86%) of product in the form of red crystals. Melting point:>260° C.,mass spectrum: 690 (M⁺ : base peak).

b) 8 g (8.82 mmol) of the compound prepared in step a), 4.14 g (44.1mmol) of phenol, 7.31 g (52.9 mmol) of potassium carbonate and 150 ml ofdimethyl sulfoxide are stirred for 9 hours at 100° C. with the exclusionof air and then cooled. The reaction mixture is then poured into 2Nhydrochloric acid and the precipitate is isolated by filtration, washedrepeatedly with water and dried. Recrystallisation from toluene gives5.33 g (69%) of the title compound, m.p.>270° C.; mass spectrum: 874(M⁺); 782 and 690 (each --C₆ H₅). A reversible colour change from yellowto red is observed by irradiating a solution of the compound in toluene.

EXAMPLE 18

2-Phenylsulfonyl-6,11-diphenoxynaphthacene-5,12-dione

4 g (7.26 mmol) of compound B3 (mixture of isomers), 5 ml of 30% aqueousH₂ O₂ and 70 ml of glacial acetic acid are stirred for 8 hours at 80° C.The mixture is taken up in a mixture of water/tetrahydrofuran/tolueneand the organic phase is separated, washed with an aqueous solution ofsodium bisulfite and twice with water, dried over sodium sulfate andconcentrated by evaporation. Recrystallisation from toluene gives 2.08 g(49%) of the title compound, m.p.>260°-270° C.; mass spectrum: 582 (M⁺ :base peak). A reversible colour change from yellow to orange is observedby irradiating a solution of the compound in toluene.

C) Use Examples EXAMPLE C1

Solutions of compounds of Examples B1 to B3 and B9 are irradiated with axenon lamp (120 W) to form the corresponding anaquinones; for example##STR18##

The anaquinones can be isolated by evaporating the solvent. Furtherparticulars are given in the following table.

    ______________________________________                                                                 UV/VIS spectrum                                      Compound      Colour     λ.sub.max (nm)                                of Example                                                                            Solvent   change     I        V                                       ______________________________________                                        B 1     toluene   yellowish  439, 469, 495                                                                          498, 552                                                  orange to red                                               B 2     toluene   yellowish  432      493, 528                                                  orange to red                                               compound                                                                              acetonitrile                                                                            yellow to red                                                                            408      467, 503                                A of B 3                                                                      compound                                                                              acetonitrile                                                                            yellow to red                                                                            393      467, 503                                B of B 3                                                                      compound                                                                              acetonitrile                                                                            yellow to red                                                                            411      469, 502                                A of B 9                                                                      compound                                                                              acetonitrile                                                                            yellow to red                                                                            395      469, 502                                B of B 9                                                                      ______________________________________                                    

EXAMPLE C2 Films prepared with inventive compounds

100 mg of polystyrene and 3.05 mg of compound A (film I) and compound Bof Example B3 (film II) are each dissolved in 8.3 g of toluene. Onefifth of each solution is poured on to heated glass plates each of 60°,70°, 80°, 90° and 100° C. and the toluene is evaporated. The films areyellow and transparent. Film I is irradiated with UV light (334 nm,laser beam, expanded to 4.5 mm) until saturated (red coloration) andplaced in the path of rays of a diode array spectrometer. Transmissionspectra are recorded periodically during irradiation with visible light(488 nm, 125 mW/cm²). The photochemical reaction is monitored on thebasis of the change of the spectrum at 470 nm. The conversion rateduring this irradiation gives a time constant of the conversion of 2.6s. A laser intensity of 25 mW/cm² at 325 nm suffices for the reversereaction for an identical speed.

Film I is irradiated at 325 nm with an intensity of 125 mJ/cm²,afterwards at 488 nm with an intensity of 625 mJ/cm². A spectrum isrecorded after every 10 cycles and compared with the spectrum before thefirst cycle. No permanent change in the sample can be measured after 150alternating exposures. The energy density necessary for thephotochemical reaction also remains the same.

EXAMPLE C3 Irradiation cycles using a polystyrene film

100 mg of polystyrene and 3 mg of compound B3 are dissolved in 8.3 g oftoluene and poured on to heated glass plate of 70° C. The solvent isevaporated off to give a yellow transparent film having a thickness of10 μm. The film is mounted on a quartz glass plate in the testingchamber of a spectrophotometer and irradiated with a 300 W xenon lampthrough glass fibers and a UV filter (Schott UG11). The integralirradiation intensity is 0.5 mW/cm². At approximately 60 s intervals theirradiation is discontinued and the absorption spectrum is measured. Thespectrum of the sample changes from yellow (optical density 1 at 300 nm,0.4 at 400 nm and zero above 450 nm) to red, caused by a broadabsorption band in the range from 400 to 550 nm (maximum optical density0.65 at 480 nm). The time constant of the conversion is 250 s. For thereverse reaction, the UV filter is replaced by a yellow cut-on filter(Schott GG 475 with transmission above ca. 450 nm). The integralirradiation intensity in the range from 450 to 550 nm is 3 mW/cm². Theirradiation causes the long-wave absorption band to disappear at 400 to550 nm to a maximum optical density of 0.1. The time constant of thereverse reaction is 200 s. In further irradiation cycles the criticalvalues of the optical density remain constant (at 480 nm: ca. 0.1/0.65).

EXAMPLE C4 Dot marking of a polystyrene film

The film of Example C3 is placed between 2 quartz glass plates on anxy-table and irradiated with UV light (excimer laser 308 nm, ca. 0.2J/cm² per pulse) until saturated (red coloration). A laser beam ofwavelength 488 nm ((Ar⁺ -ion laser) is focused pointwise on the film viaan electrooptical switch, a monomode filament and a microscopic lens.Depending on the irradiation intensity and pulse duration, thetransmission of the dots written into the film at 488 nm afterirradiation is 25% to 85%. The necessary irradiation intensity for a 50%change in transmission (25 to 75%) is 0.5 W/cm². During writing, theirradiated dots exhibit orange fluorescence (500-700 nm). For readingout the transmission of a dot, an energy which is substantially reducedcompared with that used for writing and which virtually does not changethe transmission will suffice. Renewed UV irradiation of the film (ca.0.2 J/cm² at 308 nm) erases the dots almost completely.

EXAMPLE C5 Recording a hologram

The film of Example C3 is placed between two quartz glass plates in theplane of the film of a holographic recorder and irradiated with UV lightuntil completely saturated (red coloration). With an expanded,wave-guided beam of an argon laser (488 nm) an object is projectedvertically on to the plane of the film by means of a rainbow masterhologram. A portion of the expanded beam is used as reference beam(angle of incidence ca. 30°). The irradiation intensity in the plane ofthe film is ca. 5 W/cm², diistributed between the reference and theobject beam in the ratio of 4:1. After an irradiation time of 60 s, theirradiation intensity is substantially reduced and the object beam isfaded out. The hologram recorded in the film appears with good contrastin the plane of the film. The hologram is just as clearly visible whenusing the white light of a spot lamp instead of laser light for readingout, in which case only the short-wave (blue) rainbow colours appear.Brightness and contrast of the hologram diminish after prolongedirradiation of the film under the reference beam.

EXAMPLE C6 Holographic recording

The film of Example C3 is placed between two quartz glass plates in thefilm plane of a holographic recorder. Two even beams (O and R), eachhaving an irradiation intensity of 2.5 mW/cm², are formed from anexpanded, wave-guided argon laser beam (488 nm, φ ca. 0.5 cm) andbrought to coincidence at an angle of 3° in the plane of the film. Abundle of UV light (0.5 mW/cm²), coincident with O and R, is directed onto the plane of the film from a 300 W xenon lamp through a UV filter(Schott UG11) and a quartz filament. Behind the plane of the film, adetector for measuring the diffraction efficiency is mounted in thedirection of the first order of diffraction of R and of the second of O.The film is converted into the red form by irradiating it for 10 minuteswith UV light. After activating O and R, there occurs a monotonicincrease in the diffraction efficiency from 0 to ca. 0.1% (writing) over60 s. After discontinuing O, the diffraction efficiency increasessharply to ca. 0.12% (suppression of the destructively interferingsecond diffraction order of O) and then increases approximatelyexponentially with a time constant of ca. 60 s (overwriting). Erasure iseffected by renewed UV irradiation. No diminution of the diffractionefficiency can be determined after 10 cycles. Simultaneous writing anderasing (holographic short-time memory) gives a stationary diffractionefficiency of ca. 0.05%.

What is claimed is:
 1. A compound of formula V ##STR19## wherein R isunsubstituted C₆ -C₁₄ aryl or C₆ -C₁₄ aryl which is substituted by C₁-C₁₂ alkyl, C₁ -C₁₂ alkoxy, C₁ -C₁₂ alkylthiol, phenyl, benzyl, --CN,--CF3, halogen or --COOR₅ ; and R₅ is H, C₁ -C₁₈ alkyl, cyclohexyl,cyclopentyl, phenyl, C₁ -C₁₂ alkylphenyl, benzyl or C₁ -C₁₂ alkylbenzyl;and at least one of the substituents R₁ to R₄ is an organic thiol,sulfoxy or sulfonyl group, and the other members R₁ to R₄ are H, F, Clor Br.